Semiconductor wafers are typically stored, processed and/or transported in cassettes that have a series of parallel slots, each of which receives and holds a single wafer. The cassettes are also commonly referred to as wafer "boats", particularly for those used in wet processing operations. Most wafer cassettes hold up to twenty five wafers. The gap between adjacent wafers varies between about 1/8" for six inch diameter wafers to about 1/4" for eight inch diameter wafers. During the manufacturing process, individual wafers are inscribed or imprinted with identifying information, such as lot numbers and processing and test information. This information, which is typically located along the perimeter of the wafer, must be read periodically by technicians, operators or processing machines. However, because of the close spacing of the wafers in a cassette, it is difficult to read the information without removing the wafers from the cassette or otherwise exposing the perimeter of the wafers. Manually lifting the individual wafers is time consuming and expensive and increases the risk of contaminating the wafers.
Conventional wafer lifts, such as the H-Square Corp. "Wafer Escalator", utilize a passive mechanism wherein a stationary angled contact surface engages and lifts the wafers as the cassette is lowered onto the escalator. The present invention provides an alternative to such passive devices by using an active lifting mechanism that allows the operator to raise the wafers after the cassette has been placed on the machine. Thus, the operator is able to better control the extent to which the individual wafers are raised and lowered.